It's actually illegal in the US and EU to void a warranty over aftermarket parts. The vendor must prove the aftermarket part caused the problem. If they do, they can void only the part of the warranty covering damage caused by the aftermarket part, and only until it is restored to functionality (that is, a repair restores the warranty). The Magnuson-Moss Warranty Act in the US is mostly brought up for cars, so that's where most of the caselaw is, but it actually applies to any warranty on any product sold in the US. I forget the name of the law in the EU, but it's even broader in scope.
The overwhelming majority of "Warranty void if seal broken" stickers are not binding.
To answer @Bernardes' question directly, if you have a support contract (and a 23500 is new enough to have one), it's easiest to just get drives from Check Point. If the device is already unsupported and you only care about getting it to work (e.g, to use a decommissioned box in a lab), any SATA SSD will work, but not SAS or NVMe. SATA SSDs don't all perform equally, of course. Pretty much any Intel S3_00, S3_10, S4_00, S4_10, any Samsung EVO, or any Micron drive should be great.
For anybody curious about what SSDs Check Point actually sells, I just checked 78 of my firewalls. 30 of them have a total of 40 SSDs:
- 6x Intel S4510 240 GB
- 13x Intel S4610 240 GB
- 4x Intel S4610 480 GB
- 1x Samsung SM863 240 GB
- 16x Samsung PM897 480 GB
The SM863 and one of the S4610 drives are in a pair of 6600 units ordered at the same time.